System and method for nonlinearity estimation with reference signals

ABSTRACT

A transmitter may be configured to generate a reference signal having a non-constant envelope for nonlinearity estimation by a receiver. The transmitter may transmit the reference signal. A receiver may be configured to receive, from the transmitter, the reference signal having the non-constant envelope. The receiver may estimate at least one nonlinearity characteristic based on the reference signal having the non-constant envelope. The receiver may transmit feedback based on the at least one nonlinearity characteristic and/or perform at least one digital post distortion (DPoD) operation based on the at least one nonlinearity characteristic.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No.16/222,884, entitled “SYSTEM AND METHOD FOR NONLINEARITY ESTIMATION WITHREFERENCE SIGNALS” and filed on Dec. 17, 2018, which claims the benefitof U.S. Provisional Application Ser. No. 62/607,161, entitled“NONLINEARITY ESTIMATION USING NON-CONSTANT ENVELOPE REFERENCE SIGNALS”and filed on Dec. 18, 2017, which are expressly incorporated byreference herein in their entireties.

BACKGROUND Technical Field

The present disclosure relates generally to communication systems, andmore particularly, to a transmitter configured to generate a referencesignal having a non-constant envelope that may be used for nonlinearityestimation.

Introduction

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources. Examples of suchmultiple-access technologies include code division multiple access(CDMA) systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, orthogonal frequency divisionmultiple access (OFDMA) systems, single-carrier frequency divisionmultiple access (SC-FDMA) systems, and time division synchronous codedivision multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example telecommunication standardis 5G New Radio (NR). 5G NR is part of a continuous mobile broadbandevolution promulgated by Third Generation Partnership Project (3GPP) tomeet new requirements associated with latency, reliability, security,scalability (e.g., with Internet of Things (IoT)), and otherrequirements. 5G NR includes services associated with enhanced mobilebroadband (eMBB), massive machine type communications (mMTC), and ultrareliable low latency communications (URLLC). Some aspects of 5G NR maybe based on the 4G Long Term Evolution (LTE) standard. There exists aneed for further improvements in 5G NR technology. These improvementsmay also be applicable to other multi-access technologies and thetelecommunication standards that employ these technologies.

SUMMARY

The following presents a simplified summary of one or more aspects inorder to provide a basic understanding of such aspects. This summary isnot an extensive overview of all contemplated aspects, and is intendedto neither identify key or critical elements of all aspects nordelineate the scope of any or all aspects. Its sole purpose is topresent some concepts of one or more aspects in a simplified form as aprelude to the more detailed description that is presented later.

In various wireless communications system, a transmitter may includevarious nonlinear components, such as high power amplifiers with limitlinear dynamic range. Some nonlinear components may distort atransmitted signal due to high peak to average power ratio (PAPR). Inorder to reduce this distortion, a back off may be applied (e.g., to thetransmission power). However, the back off may reduce power efficiency.

The efficiency of radiated power may be influential in the design of aradio frequency (RF) transmitter. In order to improve efficiency, atleast one digital pre-distortion (DPD) operation and/or digitalpost-distortion (DPoD) operations may be performed based onnon-linearity estimations from the transmission of the signal. Forexample, a transmitter may apply DPD operations and/or a receiver mayapply DPoD operations. In order perform DPD and/or DPoD operations, thenon-linearity characteristics of various components in the transmitterand/or the receiver (e.g., amplifiers, signal converters, etc.) may beestimated.

The present disclosure may provide approaches to estimation ofnonlinearity characteristics of various components of the transmitterand/or receiver. Various approaches described herein may avoiddata-driven nonlinearity estimation, which may use iterative decodingfor signals having a relatively high signal-to-noise ratio (SNR) andwith a modulation scheme of 16 quadrature amplitude modulation (QAM) ora higher modulation scheme. In various approaches, various portions of atransmitted signal may be used for nonlinearity estimation, such as apreamble. The dynamic range of a transmitted reference signal may bemodified using non-constant envelope constellations in order to covermany (potentially all) dynamic ranges of nonlinear components. Someapproaches described in the present disclosure may differ from someprotocols, which may use signal preambles with a constant (orapproximately constant, due to some shaping pulse) envelope in order toavoid nonlinearity effects (e.g., for a high-power amplifier). Signalpreambles with a constant (or nearly constant) envelope may preventnonlinearity estimation by a receiver.

In an aspect of the disclosure, a method, a computer-readable medium,and an apparatus are provided. The apparatus may be a transmitter. Theapparatus may generate a reference signal having a non-constant envelopefor nonlinearity estimation by a receiver. The apparatus may transmitthe reference signal, e.g., to a receiver. In an aspect, the referencesignal includes a primary synchronization signal. In an aspect, theprimary synchronization signal is based on a Zadoff-Chu sequence. In anaspect, the reference signal includes one of a short training sequence(STS) or a guard interval (GI). In an aspect, the reference signalincludes a preamble having the non-constant envelope. In an aspect, thegeneration of the reference signal having the non-constant envelopeincludes modulation of the reference signal to have a first dynamicrange, the first dynamic range being higher than a second dynamic rangeof another signal having a constant envelope. The apparatus may furtherreceive, from the receiver, feedback associated with the nonlinearityestimation, and perform at least one DPD operation based on thefeedback. In an aspect, the performance of the at least one DPDoperation based on the feedback comprises adjusting one or morecoefficients associated with at least one of a high-power amplifier(HPA) or a digital to analog converter (DAC).

In an aspect of the disclosure, a method, a computer-readable medium,and an apparatus are provided. The apparatus may be a receiver. Theapparatus may receive a reference signal having a non-constant envelope.The apparatus may estimate at least one nonlinearity characteristicbased on the reference signal having the non-constant envelope. Theapparatus may at least one of: transmit feedback based on the at leastone nonlinearity characteristic, or perform at least one DPoD operationbased on the at least one nonlinearity characteristic. In an aspect, thereference signal includes a primary synchronization signal. In anaspect, the primary synchronization signal is based on a Zadoff-Chusequence. In an aspect, the reference signal includes one of a STS or aGI. In an aspect, the reference signal includes a preamble having thenon-constant envelope. In an aspect, the estimation of the at least onenonlinearity characteristic based on the reference signal having thenon-constant envelope is based on a least-squares algorithm. In anaspect, the performance of the at least one DPoD operation based on theat least one nonlinearity characteristic comprises adjusting one or morecoefficients associated with at least one of a low-noise amplifier (LNA)or an analog to digital converter (ADC).

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed, and this description is intended to include all suchaspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network.

FIGS. 2A, 2B, 2C, and 2D are diagrams illustrating examples of a first5G/NR frame, DL channels within a 5G/NR subframe, a second 5G/NR frame,and UL channels within a 5G/NR subframe, respectively.

FIG. 3 is a diagram illustrating an example of a base station and userequipment (UE) in an access network.

FIG. 4 is a call flow diagram of a wireless communications system.

FIG. 5 is a diagram of a model of characteristics that may contribute tononlinearity.

FIG. 6 is a flowchart of a method of wireless communication.

FIG. 7 is a flowchart of a method of wireless communication.

FIG. 8 is a conceptual data flow diagram illustrating the data flowbetween different means/components in an exemplary apparatus.

FIG. 9 is a diagram illustrating an example of a hardware implementationfor an apparatus employing a processing system.

FIG. 10 is a conceptual data flow diagram illustrating the data flowbetween different means/components in an exemplary apparatus.

FIG. 11 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawings by various blocks, components, circuits,processes, algorithms, etc. (collectively referred to as “elements”).These elements may be implemented using electronic hardware, computersoftware, or any combination thereof. Whether such elements areimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented as a “processing system” thatincludes one or more processors. Examples of processors includemicroprocessors, microcontrollers, graphics processing units (GPUs),central processing units (CPUs), application processors, digital signalprocessors (DSPs), reduced instruction set computing (RISC) processors,systems on a chip (SoC), baseband processors, field programmable gatearrays (FPGAs), programmable logic devices (PLDs), state machines, gatedlogic, discrete hardware circuits, and other suitable hardwareconfigured to perform the various functionality described throughoutthis disclosure. One or more processors in the processing system mayexecute software. Software shall be construed broadly to meaninstructions, instruction sets, code, code segments, program code,programs, subprograms, software components, applications, softwareapplications, software packages, routines, subroutines, objects,executables, threads of execution, procedures, functions, etc., whetherreferred to as software, firmware, middleware, microcode, hardwaredescription language, or otherwise.

Accordingly, in one or more example embodiments, the functions describedmay be implemented in hardware, software, or any combination thereof. Ifimplemented in software, the functions may be stored on or encoded asone or more instructions or code on a computer-readable medium.Computer-readable media includes computer storage media. Storage mediamay be any available media that can be accessed by a computer. By way ofexample, and not limitation, such computer-readable media can comprise arandom-access memory (RAM), a read-only memory (ROM), an electricallyerasable programmable ROM (EEPROM), optical disk storage, magnetic diskstorage, other magnetic storage devices, combinations of theaforementioned types of computer-readable media, or any other mediumthat can be used to store computer executable code in the form ofinstructions or data structures that can be accessed by a computer.

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network 100. The wireless communications system(also referred to as a wireless wide area network (WWAN)) includes basestations 102, UEs 104, an Evolved Packet Core (EPC) 160, and a 5G Core(5GC) 190. The base stations 102 may include macro cells (high powercellular base station) and/or small cells (low power cellular basestation). The macro cells include base stations. The small cells includefemtocells, picocells, and microcells.

The base stations 102 configured for 4G LTE (collectively referred to asEvolved Universal Mobile Telecommunications System (UMTS) TerrestrialRadio Access Network (E-UTRAN)) may interface with the EPC 160 throughbackhaul links 132 (e.g., S1 interface). The base stations 102configured for 5G NR (collectively referred to as Next Generation RAN(NG-RAN)) may interface with 5GC 190 through backhaul links 184. Inaddition to other functions, the base stations 102 may perform one ormore of the following functions: transfer of user data, radio channelciphering and deciphering, integrity protection, header compression,mobility control functions (e.g., handover, dual connectivity),inter-cell interference coordination, connection setup and release, loadbalancing, distribution for non-access stratum (NAS) messages, NAS nodeselection, synchronization, radio access network (RAN) sharing,multimedia broadcast multicast service (MBMS), subscriber and equipmenttrace, RAN information management (RIM), paging, positioning, anddelivery of warning messages. The base stations 102 may communicatedirectly or indirectly (e.g., through the EPC 160 or 5GC 190) with eachother over backhaul links 134 (e.g., X2 interface). The backhaul links134 may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Eachof the base stations 102 may provide communication coverage for arespective geographic coverage area 110. There may be overlappinggeographic coverage areas 110. For example, the small cell 102′ may havea coverage area 110′ that overlaps the coverage area 110 of one or moremacro base stations 102. A network that includes both small cell andmacro cells may be known as a heterogeneous network. A heterogeneousnetwork may also include Home Evolved Node Bs (eNBs) (HeNBs), which mayprovide service to a restricted group known as a closed subscriber group(CSG). The communication links 120 between the base stations 102 and theUEs 104 may include uplink (UL) (also referred to as reverse link)transmissions from a UE 104 to a base station 102 and/or downlink (DL)(also referred to as forward link) transmissions from a base station 102to a UE 104. The communication links 120 may use multiple-input andmultiple-output (MIMO) antenna technology, including spatialmultiplexing, beamforming, and/or transmit diversity. The communicationlinks may be through one or more carriers. The base stations 102/UEs 104may use spectrum up to Y MHz (e.g., 5, 10, 15, 20, 100, 400, etc. MHz)bandwidth per carrier allocated in a carrier aggregation of up to atotal of Yx MHz (x component carriers) used for transmission in eachdirection. The carriers may or may not be adjacent to each other.Allocation of carriers may be asymmetric with respect to DL and UL(e.g., more or less carriers may be allocated for DL than for UL). Thecomponent carriers may include a primary component carrier and one ormore secondary component carriers. A primary component carrier may bereferred to as a primary cell (PCell) and a secondary component carriermay be referred to as a secondary cell (SCell).

Certain UEs 104 may communicate with each other using device-to-device(D2D) communication link 158. The D2D communication link 158 may use theDL/UL WWAN spectrum. The D2D communication link 158 may use one or moresidelink channels, such as a physical sidelink broadcast channel(PSBCH), a physical sidelink discovery channel (PSDCH), a physicalsidelink shared channel (PSSCH), and a physical sidelink control channel(PSCCH). D2D communication may be through a variety of wireless D2Dcommunications systems, such as for example, FlashLinQ, WiMedia,Bluetooth, ZigBee, Wi-Fi based on the IEEE 802.11 standard, LTE, or NR.

The wireless communications system may further include a Wi-Fi accesspoint (AP) 150 in communication with Wi-Fi stations (STAs) 152 viacommunication links 154 in a 5 GHz unlicensed frequency spectrum. Whencommunicating in an unlicensed frequency spectrum, the STAs 152/AP 150may perform a clear channel assessment (CCA) prior to communicating inorder to determine whether the channel is available.

The small cell 102′ may operate in a licensed and/or an unlicensedfrequency spectrum. When operating in an unlicensed frequency spectrum,the small cell 102′ may employ NR and use the same 5 GHz unlicensedfrequency spectrum as used by the Wi-Fi AP 150. The small cell 102′,employing NR in an unlicensed frequency spectrum, may boost coverage toand/or increase capacity of the access network.

A base station 102, whether a small cell 102′ or a large cell (e.g.,macro base station), may include an eNB, gNodeB (gNB), or other type ofbase station. Some base stations, such as gNB 180 may operate in atraditional sub 6 GHz spectrum, in millimeter wave (mmW) frequencies,and/or near mmW frequencies in communication with the UE 104. When thegNB 180 operates in mmW or near mmW frequencies, the gNB 180 may bereferred to as an mmW base station. Extremely high frequency (EHF) ispart of the RF in the electromagnetic spectrum. EHF has a range of 30GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters.Radio waves in the band may be referred to as a millimeter wave. NearmmW may extend down to a frequency of 3 GHz with a wavelength of 100millimeters. The super high frequency (SHF) band extends between 3 GHzand 30 GHz, also referred to as centimeter wave. Communications usingthe mmW/near mmW radio frequency band (e.g., 3 GHz-300 GHz) hasextremely high path loss and a short range. The mmW base station 180 mayutilize beamforming 182 with the UE 104 to compensate for the extremelyhigh path loss and short range.

The base station 180 may transmit a beamformed signal to the UE 104 inone or more transmit directions 182′. The UE 104 may receive thebeamformed signal from the base station 180 in one or more receivedirections 182″. The UE 104 may also transmit a beamformed signal to thebase station 180 in one or more transmit directions. The base station180 may receive the beamformed signal from the UE 104 in one or morereceive directions. The base station 180/UE 104 may perform beamtraining to determine the best receive and transmit directions for eachof the base station 180/UE 104. The transmit and receive directions forthe base station 180 may or may not be the same. The transmit andreceive directions for the UE 104 may or may not be the same.

The EPC 160 may include a Mobility Management Entity (MME) 162, otherMMES 164, a Serving Gateway 166, a Multimedia Broadcast MulticastService (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC)170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be incommunication with a Home Subscriber Server (HSS) 174. The MME 162 isthe control node that processes the signaling between the UEs 104 andthe EPC 160. Generally, the MME 162 provides bearer and connectionmanagement. All user Internet protocol (IP) packets are transferredthrough the Serving Gateway 166, which itself is connected to the PDNGateway 172. The PDN Gateway 172 provides UE IP address allocation aswell as other functions. The PDN Gateway 172 and the BM-SC 170 areconnected to the IP Services 176. The IP Services 176 may include theInternet, an intranet, an IP Multimedia Subsystem (IMS), a PS StreamingService, and/or other IP services. The BM-SC 170 may provide functionsfor MBMS user service provisioning and delivery. The BM-SC 170 may serveas an entry point for content provider MBMS transmission, may be used toauthorize and initiate MBMS Bearer Services within a public land mobilenetwork (PLMN), and may be used to schedule MBMS transmissions. The MBMSGateway 168 may be used to distribute MBMS traffic to the base stations102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN)area broadcasting a particular service, and may be responsible forsession management (start/stop) and for collecting eMBMS relatedcharging information.

The 5GC 190 may include a Access and Mobility Management Function (AMF)192, other AMFs 193, a Session Management Function (SMF) 194, and a UserPlane Function (UPF) 195. The AMF 192 may be in communication with aUnified Data Management (UDM) 196. The AMF 192 is the control node thatprocesses the signaling between the UEs 104 and the 5GC 190. Generally,the AMF 192 provides QoS flow and session management. All user Internetprotocol (IP) packets are transferred through the UPF 195. The UPF 195provides UE IP address allocation as well as other functions. The UPF195 is connected to the IP Services 197. The IP Services 197 may includethe Internet, an intranet, an IP Multimedia Subsystem (IMS), a PSStreaming Service, and/or other IP services.

The base station may also be referred to as a gNB, Node B, evolved NodeB (eNB), an access point, a base transceiver station, a radio basestation, a radio transceiver, a transceiver function, a basic serviceset (BSS), an extended service set (ESS), a transmit reception point(TRP), or some other suitable terminology. The base station 102 providesan access point to the EPC 160 or 5GC 190 for a UE 104. Examples of UEs104 include a cellular phone, a smart phone, a session initiationprotocol (SIP) phone, a laptop, a personal digital assistant (PDA), asatellite radio, a global positioning system, a multimedia device, avideo device, a digital audio player (e.g., MP3 player), a camera, agame console, a tablet, a smart device, a wearable device, a vehicle, anelectric meter, a gas pump, a large or small kitchen appliance, ahealthcare device, an implant, a sensor/actuator, a display, or anyother similar functioning device. Some of the UEs 104 may be referred toas IoT devices (e.g., parking meter, gas pump, toaster, vehicles, heartmonitor, etc.). The UE 104 may also be referred to as a station, amobile station, a subscriber station, a mobile unit, a subscriber unit,a wireless unit, a remote unit, a mobile device, a wireless device, awireless communications device, a remote device, a mobile subscriberstation, an access terminal, a mobile terminal, a wireless terminal, aremote terminal, a handset, a user agent, a mobile client, a client, orsome other suitable terminology.

Referring again to FIG. 1, in certain aspects, the base station 180 maybe configured to generate a reference signal 198 having a non-constantenvelope. The base station 180 may transmit the reference signal 198having the non-constant envelope to the UE 104. The UE 104 may beconfigured to receive the reference signal 198 having the non-constantenvelope from the base station 180. The UE 104 may estimate one or morenonlinearity characteristics based on the reference signal 198.Thereafter, the UE 104 may (1) transmit, to the base station 180,feedback based on the one or more nonlinearity characteristics, (2)perform at least one digital post distortion (DPoD) operation based onthe one or more nonlinearity characteristics, or (3) both transmitfeedback based on the one or more nonlinearity characteristics andperform the at least one DPoD operation based on the one or morenonlinearity characteristics. When the UE 104 transmits feedback basedon the one or more nonlinearity characteristics to the base station 180,the base station 180 may perform at least one digital pre-distortion(DPD) operation based on the feedback. In this way, the UE 104 and/orthe base station 180 may improve the response, throughput, and/orcapacity of one or more channels on which the UE 104 and the basestation 180 communicate.

FIG. 2A is a diagram 200 illustrating an example of a first subframewithin a 5G/NR frame structure. FIG. 2B is a diagram 230 illustrating anexample of DL channels within a 5G/NR subframe. FIG. 2C is a diagram 250illustrating an example of a second subframe within a 5G/NR framestructure. FIG. 2D is a diagram 280 illustrating an example of ULchannels within a 5G/NR subframe. The 5G/NR frame structure may be FDDin which for a particular set of subcarriers (carrier system bandwidth),subframes within the set of subcarriers are dedicated for either DL orUL, or may be TDD in which for a particular set of subcarriers (carriersystem bandwidth), subframes within the set of subcarriers are dedicatedfor both DL and UL. In the examples provided by FIGS. 2A, 2C, the 5G/NRframe structure is assumed to be TDD, with subframe 4 being configuredwith slot format 28 (with mostly DL), where D is DL, U is UL, and X isflexible for use between DL/UL, and subframe 3 being configured withslot format 34 (with mostly UL). While subframes 3, 4 are shown withslot formats 34, 28, respectively, any particular subframe may beconfigured with any of the various available slot formats 0-61. Slotformats 0, 1 are all DL, UL, respectively. Other slot formats 2-61include a mix of DL, UL, and flexible symbols. UEs are configured withthe slot format (dynamically through DL control information (DCI), orsemi-statically/statically through radio resource control (RRC)signaling) through a received slot format indicator (SFI). Note that thedescription infra applies also to a 5G/NR frame structure that is TDD.

Other wireless communication technologies may have a different framestructure and/or different channels. A frame (10 ms) may be divided into10 equally sized subframes (1 ms). Each subframe may include one or moretime slots. Subframes may also include mini-slots, which may include 7,4, or 2 symbols. Each slot may include 7 or 14 symbols, depending on theslot configuration. For slot configuration 0, each slot may include 14symbols, and for slot configuration 1, each slot may include 7 symbols.The symbols on DL may be cyclic prefix (CP) OFDM (CP-OFDM) symbols. Thesymbols on UL may be CP-OFDM symbols (for high throughput scenarios) ordiscrete Fourier transform (DFT) spread OFDM (DFT-s-OFDM) symbols (alsoreferred to as single carrier frequency-division multiple access(SC-FDMA) symbols) (for power limited scenarios; limited to a singlestream transmission). The number of slots within a subframe is based onthe slot configuration and the numerology. For slot configuration 0,different numerologies μ 0 to 5 allow for 1, 2, 4, 8, 16, and 32 slots,respectively, per subframe. For slot configuration 1, differentnumerologies 0 to 2 allow for 2, 4, and 8 slots, respectively, persubframe. Accordingly, for slot configuration 0 and numerology μ, thereare 14 symbols/slot and 2^(μ) slots/subframe. The subcarrier spacing andsymbol length/duration are a function of the numerology. The subcarrierspacing may be equal to 2^(μ)*15 kKz, where μ is the numerology 0 to 5.As such, the numerology μ=0 has a subcarrier spacing of 15 kHz and thenumerology μ=5 has a subcarrier spacing of 480 kHz. The symbollength/duration is inversely related to the subcarrier spacing. FIGS.2A-2D provide an example of slot configuration 0 with 14 symbols perslot and numerology μ=0 with 1 slot per subframe. The subcarrier spacingis 15 kHz and symbol duration is approximately 66.7 μs.

A resource grid may be used to represent the frame structure. Each timeslot includes a resource block (RB) (also referred to as physical RBs(PRBs)) that extends 12 consecutive subcarriers. The resource grid isdivided into multiple resource elements (REs). The number of bitscarried by each RE depends on the modulation scheme.

As illustrated in FIG. 2A, some of the REs carry reference (pilot)signals (RS) for the UE. The RS may include demodulation RS (DM-RS)(indicated as R_(x) for one particular configuration, where 100× is theport number, but other DM-RS configurations are possible) and channelstate information reference signals (CSI-RS) for channel estimation atthe UE. The RS may also include beam measurement RS (BRS), beamrefinement RS (BRRS), and phase tracking RS (PT-RS).

FIG. 2B illustrates an example of various DL channels within a subframeof a frame. The physical downlink control channel (PDCCH) carries DCIwithin one or more control channel elements (CCEs), each CCE includingnine RE groups (REGs), each REG including four consecutive REs in anOFDM symbol. A primary synchronization signal (PSS) may be within symbol2 of particular subframes of a frame. The PSS is used by a UE 104 todetermine subframe/symbol timing and a physical layer identity. Asecondary synchronization signal (SSS) may be within symbol 4 ofparticular subframes of a frame. The SSS is used by a UE to determine aphysical layer cell identity group number and radio frame timing. Basedon the physical layer identity and the physical layer cell identitygroup number, the UE can determine a physical cell identifier (PCI).Based on the PCI, the UE can determine the locations of theaforementioned DM-RS. The physical broadcast channel (PBCH), whichcarries a master information block (MIB), may be logically grouped withthe PSS and SSS to form a synchronization signal (SS)/PBCH block. TheMIB provides a number of RBs in the system bandwidth and a system framenumber (SFN). The physical downlink shared channel (PDSCH) carries userdata, broadcast system information not transmitted through the PBCH suchas system information blocks (SIBs), and paging messages.

As illustrated in FIG. 2C, some of the REs carry DM-RS (indicated as Rfor one particular configuration, but other DM-RS configurations arepossible) for channel estimation at the base station. The UE maytransmit DM-RS for the physical uplink control channel (PUCCH) and DM-RSfor the physical uplink shared channel (PUSCH). The PUSCH DM-RS may betransmitted in the first one or two symbols of the PUSCH. The PUCCHDM-RS may be transmitted in different configurations depending onwhether short or long PUCCHs are transmitted and depending on theparticular PUCCH format used. Although not shown, the UE may transmitsounding reference signals (SRS). The SRS may be used by a base stationfor channel quality estimation to enable frequency-dependent schedulingon the UL.

FIG. 2D illustrates an example of various UL channels within a subframeof a frame. The PUCCH may be located as indicated in one configuration.The PUCCH carries uplink control information (UCI), such as schedulingrequests, a channel quality indicator (CQI), a precoding matrixindicator (PMI), a rank indicator (RI), and HARQ ACK/NACK feedback. ThePUSCH carries data, and may additionally be used to carry a bufferstatus report (BSR), a power headroom report (PHR), and/or UCI.

FIG. 3 is a block diagram of a base station 310 in communication with aUE 350 in an access network. In the DL, IP packets from the EPC 160 maybe provided to a controller/processor 375. The controller/processor 375implements layer 3 and layer 2 functionality. Layer 3 includes a radioresource control (RRC) layer, and layer 2 includes a service dataadaptation protocol (SDAP) layer, a packet data convergence protocol(PDCP) layer, a radio link control (RLC) layer, and a medium accesscontrol (MAC) layer. The controller/processor 375 provides RRC layerfunctionality associated with broadcasting of system information (e.g.,MIB, SIBs), RRC connection control (e.g., RRC connection paging, RRCconnection establishment, RRC connection modification, and RRCconnection release), inter radio access technology (RAT) mobility, andmeasurement configuration for UE measurement reporting; PDCP layerfunctionality associated with header compression/decompression, security(ciphering, deciphering, integrity protection, integrity verification),and handover support functions; RLC layer functionality associated withthe transfer of upper layer packet data units (PDUs), error correctionthrough ARQ, concatenation, segmentation, and reassembly of RLC servicedata units (SDUs), re-segmentation of RLC data PDUs, and reordering ofRLC data PDUs; and MAC layer functionality associated with mappingbetween logical channels and transport channels, multiplexing of MACSDUs onto transport blocks (TBs), demultiplexing of MAC SDUs from TBs,scheduling information reporting, error correction through HARQ,priority handling, and logical channel prioritization.

The transmit (TX) processor 316 and the receive (RX) processor 370implement layer 1 functionality associated with various signalprocessing functions. Layer 1, which includes a physical (PHY) layer,may include error detection on the transport channels, forward errorcorrection (FEC) coding/decoding of the transport channels,interleaving, rate matching, mapping onto physical channels,modulation/demodulation of physical channels, and MIMO antennaprocessing. The TX processor 316 handles mapping to signalconstellations based on various modulation schemes (e.g., binaryphase-shift keying (BPSK), quadrature phase-shift keying (QPSK),M-phase-shift keying (M-PSK), M-quadrature amplitude modulation(M-QAM)). The coded and modulated symbols may then be split intoparallel streams. Each stream may then be mapped to an OFDM subcarrier,multiplexed with a reference signal (e.g., pilot) in the time and/orfrequency domain, and then combined together using an Inverse FastFourier Transform (IFFT) to produce a physical channel carrying a timedomain OFDM symbol stream. The OFDM stream is spatially precoded toproduce multiple spatial streams. Channel estimates from a channelestimator 374 may be used to determine the coding and modulation scheme,as well as for spatial processing. The channel estimate may be derivedfrom a reference signal and/or channel condition feedback transmitted bythe UE 350. Each spatial stream may then be provided to a differentantenna 320 via a separate transmitter 318TX. Each transmitter 318TX maymodulate an RF carrier with a respective spatial stream fortransmission.

At the UE 350, each receiver 354RX receives a signal through itsrespective antenna 352. Each receiver 354RX recovers informationmodulated onto an RF carrier and provides the information to the receive(RX) processor 356. The TX processor 368 and the RX processor 356implement layer 1 functionality associated with various signalprocessing functions. The RX processor 356 may perform spatialprocessing on the information to recover any spatial streams destinedfor the UE 350. If multiple spatial streams are destined for the UE 350,they may be combined by the RX processor 356 into a single OFDM symbolstream. The RX processor 356 then converts the OFDM symbol stream fromthe time-domain to the frequency domain using a Fast Fourier Transform(FFT). The frequency domain signal comprises a separate OFDM symbolstream for each subcarrier of the OFDM signal. The symbols on eachsubcarrier, and the reference signal, are recovered and demodulated bydetermining the most likely signal constellation points transmitted bythe base station 310. These soft decisions may be based on channelestimates computed by the channel estimator 358. The soft decisions arethen decoded and deinterleaved to recover the data and control signalsthat were originally transmitted by the base station 310 on the physicalchannel. The data and control signals are then provided to thecontroller/processor 359, which implements layer 3 and layer 2functionality.

The controller/processor 359 can be associated with a memory 360 thatstores program codes and data. The memory 360 may be referred to as acomputer-readable medium. In the UL, the controller/processor 359provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, and control signalprocessing to recover IP packets from the EPC 160. Thecontroller/processor 359 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

Similar to the functionality described in connection with the DLtransmission by the base station 310, the controller/processor 359provides RRC layer functionality associated with system information(e.g., MIB, SIBs) acquisition, RRC connections, and measurementreporting; PDCP layer functionality associated with headercompression/decompression, and security (ciphering, deciphering,integrity protection, integrity verification); RLC layer functionalityassociated with the transfer of upper layer PDUs, error correctionthrough ARQ, concatenation, segmentation, and reassembly of RLC SDUs,re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; andMAC layer functionality associated with mapping between logical channelsand transport channels, multiplexing of MAC SDUs onto TBs,demultiplexing of MAC SDUs from TBs, scheduling information reporting,error correction through HARQ, priority handling, and logical channelprioritization.

Channel estimates derived by a channel estimator 358 from a referencesignal or feedback transmitted by the base station 310 may be used bythe TX processor 368 to select the appropriate coding and modulationschemes, and to facilitate spatial processing. The spatial streamsgenerated by the TX processor 368 may be provided to different antenna352 via separate transmitters 354TX. Each transmitter 354TX may modulatean RF carrier with a respective spatial stream for transmission.

The UL transmission is processed at the base station 310 in a mannersimilar to that described in connection with the receiver function atthe UE 350. Each receiver 318RX receives a signal through its respectiveantenna 320. Each receiver 318RX recovers information modulated onto anRF carrier and provides the information to a RX processor 370.

The controller/processor 375 can be associated with a memory 376 thatstores program codes and data. The memory 376 may be referred to as acomputer-readable medium. In the UL, the controller/processor 375provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover IP packets from the UE 350. IP packets from thecontroller/processor 375 may be provided to the EPC 160. Thecontroller/processor 375 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

In various wireless communications system, a transmitter may includevarious nonlinear components, such as high power amplifiers with limitlinear dynamic range. Some nonlinear components may distort atransmitted signal due to high peak to average power ratio (PAPR). Inorder to reduce this distortion, a back off may be applied (e.g., to thetransmission power). However, the back off may reduce power efficiency.

The efficiency of radiated power may be influential in the design of aradio frequency (RF) transmitter. In order to improve efficiency, atleast one DPD and/or at least one DPoD operation(s) may be performedbased on non-linearity estimations from the transmission of the signal.For example, a transmitter may apply at least one DPD operation and/or areceiver may apply at least one DPoD operation. In order perform atleast one DPD operation and/or at least one DPoD operation, thenon-linearity characteristics of various components in the transmitterand/or the receiver (e.g., amplifiers, signal converters, etc.) may beestimated.

The present disclosure may provide approaches to estimation ofnonlinearity characteristics of various components of the transmitterand/or receiver. Various approaches described herein may avoiddata-driven nonlinearity estimation, which may use iterative decodingfor signals having a relatively high signal-to-noise ratio (SNR) andwith a modulation scheme of 16 quadrature amplitude modulation (QAM) ora higher modulation scheme. In various approaches, various portions of atransmitted signal may be used for nonlinearity estimation, such as apreamble. The dynamic range of a transmitted reference signal may bemodified using non-constant envelope constellations in order to covermany (potentially all) dynamic ranges of nonlinear components. Someapproaches described in the present disclosure may differ from someprotocols, which may use signal preambles with a constant (orapproximately constant, due to some shaping pulse) envelope in order toavoid nonlinearity effects (e.g., for a high-power amplifier). Signalpreambles with a constant (or nearly constant) envelope may preventnonlinearity estimation by a receiver.

FIG. 4 is a call flow diagram of a wireless communications system 400.The wireless communications system 400 may include at least onetransmitter 402 and at least one receiver 404. The transmitter 402 andthe receiver 404 are illustrated as a base station and a UE,respectively (e.g., for uplink communication); however, this arrangementis to be regarded as illustrative and the transmitter 402 and/or thereceiver 404 may be any apparatuses configured for wirelesscommunication.

The transmitter 402 and the receiver 404 may be configured tocommunicate on one or more channels according to at least one standard.For example, the transmitter 402 and the receiver 404 may be configuredto communicate according to one or more 3GPP standards (e.g., 5G NR,LTE, etc.). In another example, the transmitter 402 and the receiver 404may be configured to communicate according to one or more IEEE standards(e.g., 802.11). The aforementioned examples are intended to beillustrative, and the aspects described herein may be applicable to anystandard and/or protocol for wireless communication.

In order to improve communication between the transmitter 402 and thereceiver 404, it may be beneficial to estimate one or more nonlinearitycharacteristics (or coefficients) associated with thetransmitter/receiver path (e.g., channel). Estimation of the one or morenonlinearity characteristics may allow the transmitter 402 to perform atleast one DPD operation based on feedback from the receiver 404 and/ormay allow the receiver 404 to perform at least one DPoD operation basedon the estimation of the one or more nonlinearity characteristics by thereceiver 404. In so performing at least one DPD operation and/or atleast one DPoD operation, the transmitter 402 and/or the receiver 404may improve throughput, capacity, and/or response of a channel whilealso improving efficiency of radiated power.

The transmitter 402 may include one or more nonlinear components, forexample, as part of the transmit chain corresponding to generation ofsignals for transmission. Examples of such nonlinear components includea high-power amplifier (HPA) (e.g., an HPA with limited linear dynamicrange), a digital-to-analog converter (DAC), and so forth. The nonlinearcomponents may distort signals transmitted by the transmitter 402—e.g.,an HPA with limited linear dynamic range may distort transmitted signalsdue to a relatively high peak-to-average-power ratio (PAPR).

Complementary to the transmit chain, the receiver 404 may include areceive chain. The receive chain may include one or more nonlinearcomponents. Examples of such nonlinear components include a low-noiseamplifier (LNA), an analog-to-digital converter (ADC), and so forth.

Such nonlinear components may be adjusted before transmission (e.g., atleast one DPD operation by the transmitter 402) and/or after reception(e.g., at least one DPoD operation by the receiver 404), e.g., byadjusting one or more coefficients of one or more nonlinear componentsin order to reduce or cancel distortion. In order to reduce or cancelthe distortion through at least one DPD operation and/or at least oneDPoD operation, the receiver 404 may determine (e.g., estimate) one ormore nonlinearity characteristics based on a signal having anon-constant envelope from the transmitter 402.

According to aspects, the transmitter 402 may generate 420 a referencesignal 422 having a non-constant envelope for nonlinearity estimation bythe receiver 404. In aspects, an envelope of a signal may outlinevariation of amplitude (e.g., over a period of time). A signal having aconstant envelope may have an approximately constant amplitude, e.g., sothat the absolute value of the signal is approximately one (1).Consequently, a signal having a non-constant envelope may be a signalthat may not have an approximately constant amplitude, e.g., so that theabsolute value of the signal is not approximately one (1). For example,the transmitter 402 may refrain from attempting to constrain theabsolute value of the reference signal 422 to approximately one (1),which may result in the reference signal 422 having a non-constantenvelope.

In one aspect, the transmitter 402 may set the modulation of thereference signal 422 to have a relatively higher dynamic range (e.g., ahigher dynamic range relative to a signal modulated to have a dynamicrange corresponding to a constant envelope). For example, thetransmitter 402 may set the modulation of the reference signal 422 tohave the highest possible dynamic range achievable by the transmit chain(e.g., HPA, DAC, etc.), which may enable the receiver 404 to estimate anapproximately full set of nonlinearity characteristic(s).

By way of example, the reference signal 422 may be illustrated as aplurality of samples as shown in FIG. 4. In one aspect, the transmitter402 may modulate the reference signal 422 using QAM. For example, thereference signal 422 may be a 16 QAM constellation, a 64 QAMconstellation, a 256 QAM constellation, and so forth (n.b., thereference signal 422 may be a constellation of any order QAM, and thepreceding 16, 64, and 256 orders are to be regarded as illustrative). Inanother aspect, the transmitter 402 may modulate the reference signal422 using another modulation scheme.

In one example, the reference signal 422 may include at least a portionof a downlink signal or an uplink signal (e.g., the reference signal 422may be included as part of a frame, subframe, or another transmissiontime interval (TTI)). In one example, the reference signal 422 mayinclude an individual signal (e.g., the reference signal 422 may includean individual burst of bursty communication). In one example, thereference signal 422 may include a single-carrier signal.

In various aspects, the reference signal 422 may include a knownreference signal, e.g., as defined in one or more standards and/orprotocols for wireless communication. For example, a known referencesignal may be modulated using phase-shift keying according to one ormore standards and/or protocols, such as binary phase-shift keying(BPSK). However, as indicated supra, the transmitter 402 may modulatethe reference signal 422 so that the reference signal 422 has anon-constant envelope. Thus, while the reference signal 422 may beknown, the reference signal 422 may not have a constant envelope (e.g.,the reference signal 422 would otherwise have a constant envelope whendefined by one or more known standards and/or protocols). In someaspects, the reference signal 422 having the non-constant envelope mayhave the approximately the same average power as a known referencesignal having a constant envelope.

In one example, the reference signal 422 may include a preamble thatbegins a signal. In one example, the reference signal 422 may be anotherpart of a signal besides the preamble, such as a guard period (GP) orguard interval (GI). In one example, the reference signal 422 mayinclude a pilot signal (e.g., LTE pilot signal, 5G pilot signal, WiFipilot signal, etc.). In one example, the reference signal 422 mayinclude a preamble having the non-constant envelope, and thenon-constant envelope may be absent from a second portion of thereference signal 422 that is separate from the preamble.

In the context of IEEE standard(s), including 802.11, the referencesignal 422 may include a short training sequence (STS), channelestimation sequence (CES), GI (e.g., for 802.11.ad/802.11.ay), oranother sequence. In the context of 3GPP standard(s), including 5Gand/or LTE, the reference signal 422 may include a synchronizationsignal (e.g., PSS), a Zadoff-Chu sequence, or another sequence.

As illustrated in FIG. 4, the transmitter 402 may transmit the referencesignal 422 for nonlinearity estimation by the receiver 404. The receiver404 may receive the reference signal 422 having the non-constantenvelope.

Because the reference signal 422 may be defined by one or more standardsand/or protocols, the reference signal 422 may be known by the receiver404. Upon reception, the receiver 404 may estimate 424 one or morenonlinearity characteristics (e.g., coefficients) based on the referencesignal 422 having the non-constant envelope.

In one aspect, the receiver 404 may estimate 424 the one or morenonlinearity characteristics based on an algorithm that employs theleast squares method. By way of example, the receiver 404 may estimatethe nonlinearity characteristic(s) as k_(NL)=(x_(NL) ^(H)x_(NL))⁻¹x_(NL)^(H)y. In the preceding equation, x may denote the transmitted referencesignal 422 having the non-constant envelope. Correspondingly, y maydenote the received reference signal 422, which may be modeled asy=k_(NL)x_(NL)+n (where n is noise). The nonlinearity kernels may bedenoted as x_(NL)=[x, x∥x∥², x|x|⁴]^(H) (although any order ofnonlinearity estimation can be achieved by adding additional kernels).The nonlinearity coefficients to be estimated may be denoted ask_(NL)=[k₁, k₃, k₅]. Therefore, as shown supra, the receiver 404 mayestimate 424 nonlinearity characteristic(s) or coefficient(s) ask_(NL)=(x_(NL) ^(H)x_(NL))⁻¹x_(NL) ^(H)y. The preceding examples are tobe regarded as illustrative and, therefore, the receiver 404 may employany suitable algorithm(s) in order to estimate 424 the one or morenonlinearity characteristic(s).

Based on estimation 424 of the one or more nonlinearitycharacteristic(s), the receiver 404 may perform one or more operationsin order to reduce (or cancel) nonlinearity by at least one of thetransmitter 402 and/or the receiver 404.

In one aspect, the receiver 404 may generate feedback 426 that indicatesat least one of the one or more nonlinearity characteristics. Forexample, the receiver 404 may identify the non-constant envelope of thereference signal 422, which may include identifying or detectingdistortion present in the reference signal 422. The receiver 404 maygenerate the feedback 426 to indicate the non-constant envelope (e.g.,to indicate distortion present in the received reference signal 422).The receiver 404 may transmit the generated feedback 426 to thetransmitter 402.

Responsively, the transmitter 402 may attempt to reduce (e.g., cancel)nonlinearity based on the received feedback 426. For example, thetransmitter 402 may identify the non-constant envelope (e.g., distortionin the reference signal 422 received by the receiver 404) indicated bythe feedback 426, and the transmitter 402 may perform one or moreoperations to improve reduce distortion of transmitted signals based onthe non-constant envelope indicated by the feedback 426. The transmitter402 may perform 428 at least one DPD operation based on the feedback426. In one example, the transmitter 402 may adjust one or morecoefficients or parameters of one or more components of the transmitchain of the transmitter 402. For example, the transmitter 402 mayadjust one or more coefficients associated with at least one of an HPAand/or a DAC based on the received feedback 426.

In one aspect, the receiver 404 may attempt to reduce (e.g., cancel)nonlinearity based on the estimated nonlinearity characteristic(s). Forexample, the receiver 404 may perform 430 at least one DPoD operationbased on the estimated nonlinearity characteristic(s). In one example,the receiver 404 may adjust one or more coefficients or parameters ofone or more components of the receive chain of the receiver 404. Forexample, the receiver 404 may adjust one or more coefficients associatedwith at least one of an LNA and/or an ADC based on the estimatednonlinearity characteristic(s).

In one aspect, the receiver 404 and transmitter 402 may attempt toreduce (e.g., cancel) nonlinearity at both the receiver 404 and thetransmitter 402. Accordingly, the receiver 404 may both transmit thefeedback 426 based on the nonlinearity characteristic(s) so that thetransmitter 402 may perform 428 at least one DPD operation based on thefeedback 426, and may perform 430 at least one DPoD operation based onthe nonlinearity characteristic(s).

With the operations described supra, nonlinearity may be reduced orcanceled. The reduction or cancellation of nonlinearity may improvecommunication between the transmitter 402 and the receiver 404, e.g., byimproving throughput, capacity, and/or response of at least one channelon which the transmitter 402 and the receiver 404 communicate in thewireless communications system 400.

This approach to reduction or cancellation of nonlinearity may reducethe overhead commensurate with existing approaches to nonlinearityreduction or cancellation. For example, existing approaches tononlinearity reduction or cancellation may be data-driven, may involveiterative decoding, may be effective only for a relatively high SNR, andmay be possible only for QAM modulation of an order that is sixteen (16)or higher. Advantageously, operations for nonlinearity reduction orcancellation as described herein may be more power efficient, lesscomputationally expensive (e.g., less complex, reduce or removeiterative decoding, etc.), more robust (e.g., effective for a larger SNRrange, effective for more and/or other order modulation schemes, etc.),and/or faster than existing approaches to nonlinearity reduction orcancellation.

FIG. 5 is a diagram of a HPA characteristics 500, modeled using two (2)parameters. In FIG. 5, amplitude-to-amplitude (AM/AM) modeling of amemoryless HPA is illustrated, using feedback of a sharpness factor, andsimilar modeling may be done for amplitude-to-phase (AM/PM).

${F(\rho)} = \frac{\rho}{\left( {1 + \left( \frac{\rho}{V_{cc}} \right)^{2 \cdot \rho}} \right)^{\frac{1}{2 \cdot \rho}}}$$V_{cc} = \sqrt{P_{sat}}$

In aspects, ρ may denote a coefficient, such as a voltage coefficient.In one example, ρ may be a coefficient adjusted by the transmitter 402in the transmit chain (e.g., a coefficient of an HPA), e.g., in order toreduce or cancel nonlinearity. P_(sat) may denote power, e.g., when anHPA is saturated. V_(cc) may denote voltage (e.g., power supply voltage,which may be positive). Accordingly, F(ρ) may denote the output of acomponent of a transmit chain of the transmitter 402, such as an HPA.

In FIG. 5, a first graph 520 illustrates an example for a solid statepower amplifier (SSPA) AM/AM model with V_(cc)=3. A first curve 522illustrates ρ=2.5. A second curve 524 illustrates ρ=2.1. A third curve526 illustrates ρ=1.7. A fourth curve 528 illustrates ρ=1.4. A fifthcurve 530 illustrates ρ=1.1. A sixth curve 532 illustrates ρ=0.7. Aseventh curve 534 illustrates ρ=0.5.

A second graph 540 illustrates an example of an AM/AM model that may bemeasured. A measured curve 542 may illustrate a measured F(ρ). A modeledcurve 544 may illustrate a modeled F(ρ), with ρ=2.2 and V_(cc)=1.4. Asillustrated, the modeled curve 544 approximates the measured curve 542.

FIG. 6 is a flowchart illustrating a method 600 of wirelesscommunication, in accordance with various aspects of the presentdisclosure. The method 600 may be implemented by a transmitter, such asthe transmitter 402 of FIG. 4, the base station 310 of FIG. 3, and/orthe base station 180 of FIG. 1. In various aspects, one or moreoperations may be optional (e.g., as denoted by dashed lines). Further,one or more operations may be omitted, transposed, and/orcontemporaneously performed.

Beginning at operation 602, the transmitter may generate a referencesignal having a non-constant envelope for nonlinearity estimation by areceiver. In one aspect, the reference signal may include a PSS. In oneaspect, the reference signal may be based on a sequence, such as aZadoff-Chu sequence. In one aspect, the reference signal may include atleast one of an STS or a GI. In an aspect, the reference signal includesa preamble having the non-constant envelope, and the non-constantenvelope may be absent from a second portion of the reference signalthat is separate from the preamble. In the context of FIG. 4, thetransmitter 402 may generate the reference signal 422 having anon-constant envelope for nonlinearity estimation by the receiver 404.

In one aspect, operation 602 includes operation 620. At operation 620,the transmitter may modulate the reference signal to have a firstdynamic range, and the first dynamic range may be relatively higher thana second dynamic range of another signal having a constant envelope. Forexample, the second dynamic range may correspond to the dynamic range ofa known reference signal having a constant envelope. In the context ofFIG. 4, the transmitter 402 may modulate the reference signal 422 tohave a first dynamic range, which may be relatively higher than a seconddynamic range of another reference signal having a constant envelope.

At operation 604, the transmitter may transmit the reference signal. Inone aspect, the transmitter may broadcast the reference signal. Inanother aspect, the transmitter may unicast or multicast the referencesignal to the receiver. In the context of FIG. 4, the transmitter 402may transmit the reference signal 422.

At operation 606, the transmitter may receive, from the receiver,feedback associated with the nonlinearity estimation. For example, thefeedback may indicate one or more nonlinearity characteristics orcoefficients estimated by the receiver based on the reference signalhaving the non-constant envelope. In the context of FIG. 4, thetransmitter 402 may receive, from the receiver 404, the feedback 426associated with the estimation 424 of the one or more nonlinearitycharacteristics by the receiver 404.

At operation 608, the transmitter may perform at least one DPD operationbased on the received feedback. In one aspect, the at least one DPDoperation may include an algorithm that is to be applied to one or morecomponents (e.g., RF frontend components). For example, transmitter mayidentify one or more coefficients associated with a component of thetransmitter. The component may include, e.g., an amplifier, a converter,or another component that may affect, transform, adjust, etc. a signalthat is to be transmitted. The transmitter may apply a DPD algorithm inorder to reduce distortion introduced to the signal by the component,reduce nonlinearity of the component, and/or otherwise improve signalfidelity during signal transmission. In application of the algorithm,the transmitter may calculate one or more coefficients of the componentthat may affect the signal. The calculated coefficients may be used fortransmission of one or more signals, e.g., after the signal having thenon-constant envelope. In the context of FIG. 4, the transmitter 402 mayperform 428 at least one DPD operation based on the received feedback426.

In one aspect, operation 608 includes operation 622. At operation 622,the transmitter may adjust one or more coefficients associated with oneor more components of the transmit chain of the transmitter. Forexample, the transmitter may identify at least one coefficient of an HPAand/or a DAC that contributes to the nonlinearity based on the feedback,and the transmitter may set the at least one coefficient to a valuebased on the received feedback in order to reduce or cancel nonlinearity(e.g., in order to improve signal fidelity). In the context of FIG. 4,the transmitter 402 may adjust one or more coefficients associated withat least one of an HPA or a DAC based on the received feedback 426.

FIG. 7 is a flowchart illustrating a method 700 of wirelesscommunication, in accordance with various aspects of the presentdisclosure. The method 700 may be implemented by a receiver, such as thereceiver 404 of FIG. 4, the UE 350 of FIG. 3, and/or the UE 104 ofFIG. 1. In various aspects, one or more operations may be optional(e.g., as denoted by dashed lines). Further, one or more operations maybe omitted, transposed, and/or contemporaneously performed.

Beginning with operation 702, the receiver may receive a referencesignal having a non-constant envelope. In one aspect, the referencesignal may include a PSS. In one aspect, the reference signal may bebased on a sequence, such as a Zadoff-Chu sequence. In one aspect, thereference signal may include at least one of an STS or a GI. In anaspect, the reference signal includes a preamble having the non-constantenvelope, and the non-constant envelope may be absent from a secondportion of the reference signal that is separate from the preamble. Inthe context of FIG. 4, the receiver 404 may receive the reference signal422 from the transmitter 402.

At operation 704, the receiver may estimate at least one nonlinearitycharacteristic based on the reference signal having the non-constantenvelope. In one aspect, the receiver may estimate the at least onenonlinearity characteristic using an algorithm that is based on a leastsquares method. In the context of FIG. 4, the receiver 404 may estimate424 at least one nonlinearity characteristic based on the referencesignal 422 having the non-constant envelope.

At operation 706, the receiver may transmit, to the transmitter,feedback based on the at least one nonlinearity characteristic. Forexample, the receiver may select one or more values indicative of theone or more nonlinearity characteristics, and the receiver may includethe one or more values in a message to be transmitted to the transmitterso that the transmitter may perform at least one DPD operation to reduceor cancel nonlinearity. In the context of FIG. 4, the receiver 404 maytransmit, to the transmitter 402, the feedback 426 that is based on theestimation 424 of the one or more nonlinearity characteristics.

At operation 708, the receiver may perform at least one DPoD operationbased on the at least one nonlinearity characteristic estimated by thereceiver. In one aspect, the at least one DPoD operation may include analgorithm that is to be applied to one or more components (e.g., RFfrontend components). For example, receiver may identify one or morecoefficients associated with a component of the receiver. The componentmay include, e.g., an amplifier, a converter, or another component thatmay affect, transform, adjust, etc. a signal that is to be received. Thereceiver may apply a DPoD algorithm in order to reduce distortionintroduced to the signal by the component, reduce nonlinearity of thecomponent, and/or otherwise improve signal fidelity during signalreception. In application of the algorithm, the receiver may calculateone or more coefficients of the component that may affect the signal.The calculated coefficients may be used for reception of one or moresignals, e.g., after the signal having the non-constant envelope. In thecontext of FIG. 4, the receiver 404 may perform 430 at least one DPoDoperation based on the estimation 424 of the at least one nonlinearitycharacteristic.

In one aspect, operation 708 includes operation 720. At operation 720,the receiver may adjust one or more coefficients associated with one ormore components of the receive chain of the receiver. For example, thereceiver may identify at least one coefficient of an LNA and/or an ADCthat contributes to the nonlinearity based on the estimated nonlinearitycharacteristic(s), and the receiver may set the at least one coefficientto a value based on the estimated nonlinearity characteristic(s) inorder to reduce or cancel nonlinearity. In the context of FIG. 4, thereceiver 404 may adjust one or more coefficients associated with atleast one of an LNA or an ADC based on the estimated nonlinearitycharacteristic(s).

As described, supra, the receiver may perform at least one of operation706 and operation 708. Accordingly, at least one of the transmitter orthe receiver may attempt to reduce or cancel nonlinearity by performingat least one DPD operation and/or at least one DPoD operation,respectively. Thus, in one aspect, operation 706 may be performed andoperation 708 may be omitted. In another aspect, operation 706 may beomitted and operation 708 may be performed. In a third aspect, bothoperation 706 and operation 708 may be performed (n.b., operation 706and operation 708 may be transposed in one aspect).

FIG. 8 is a conceptual data flow diagram 800 illustrating the data flowbetween different means/components in an exemplary apparatus 802. Theapparatus may be a transmitter, such as a base station. The apparatus802 includes a reception component 804 for receiving signals from a UE850. The apparatus 802 includes a transmission component 810 fortransmitting signals to the UE 850.

A signal component 806 may generate a reference signal having anon-constant envelope. The signal may be generated for nonlinearityestimation by the UE 850. In one aspect, the reference signal mayinclude a PSS. In one aspect, the PSS may be based on a Zadoff-Chusequence. The signal component 806 may generate the reference signal toinclude one of a STS and/or a GI. The signal component 806 may generatethe reference signal so that the non-constant envelope is applied to apreamble of the reference signal.

The signal component 806 may generate the reference signal to have thenon-constant envelope by modulating the reference signal to have a firstdynamic range. The first dynamic range may be higher than a seconddynamic range of another signal having a constant envelope, which mayalso be generated by the signal component 806.

The signal component 806 may provide the reference signal to thetransmission component 810 for transmission to the UE 850. The UE 850may receive the signal, and the UE 850 may transmit feedback associatedwith nonlinearity estimation based on the reference signal.

The reception component 804 may receive the feedback and provide thefeedback to the feedback component 808. The feedback component 808 mayperform at least one DPD operation based on the received feedback. Forexample, the feedback component 808 may adjust one or more coefficientsassociated with at least one of an HPA and/or a DAC of the apparatus802. The adjusted coefficients may be used for the transmission ofadditional signals.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowcharts of FIG. 6. Assuch, each block in the aforementioned flowcharts of FIG. 6 may beperformed by a component and the apparatus may include one or more ofthose components. The components may be one or more hardware componentsspecifically configured to carry out the stated processes/algorithm,implemented by a processor configured to perform the statedprocesses/algorithm, stored within a computer-readable medium forimplementation by a processor, or some combination thereof.

FIG. 9 is a diagram 900 illustrating an example of a hardwareimplementation for an apparatus 802′ employing a processing system 914.The processing system 914 may be implemented with a bus architecture,represented generally by the bus 924. The bus 924 may include any numberof interconnecting buses and bridges depending on the specificapplication of the processing system 914 and the overall designconstraints. The bus 924 links together various circuits including oneor more processors and/or hardware components, represented by theprocessor 904, the components 804, 806, 808, 810 and thecomputer-readable medium/memory 906. The bus 924 may also link variousother circuits such as timing sources, peripherals, voltage regulators,and power management circuits, which are well known in the art, andtherefore, will not be described any further.

The processing system 914 may be coupled to a transceiver 910. Thetransceiver 910 is coupled to one or more antennas 920. The transceiver910 provides a means for communicating with various other apparatus overa transmission medium. The transceiver 910 receives a signal from theone or more antennas 920, extracts information from the received signal,and provides the extracted information to the processing system 914,specifically the reception component 804. In addition, the transceiver910 receives information from the processing system 914, specificallythe transmission component 810, and based on the received information,generates a signal to be applied to the one or more antennas 920. Theprocessing system 914 includes a processor 904 coupled to acomputer-readable medium/memory 906. The processor 904 is responsiblefor general processing, including the execution of software stored onthe computer-readable medium/memory 906. The software, when executed bythe processor 904, causes the processing system 914 to perform thevarious functions described supra for any particular apparatus. Thecomputer-readable medium/memory 906 may also be used for storing datathat is manipulated by the processor 904 when executing software. Theprocessing system 914 further includes at least one of the components804, 806, 808. The components may be software components running in theprocessor 904, resident/stored in the computer readable medium/memory906, one or more hardware components coupled to the processor 904, orsome combination thereof. The processing system 914 may be a componentof the base station 310 and may include the memory 376 and/or at leastone of the TX processor 316, the RX processor 370, and thecontroller/processor 375.

In one configuration, the apparatus 802/802′ for wireless communicationincludes means for generating, by the apparatus 802/802′, a referencesignal having a non-constant envelope for nonlinearity estimation by areceiver. The apparatus 802/802′ may include means for transmitting, bythe apparatus, the reference signal. In one aspect, the reference signalcomprises a primary synchronization signal. In one aspect, the primarysynchronization signal is based on a Zadoff-Chu sequence. In one aspect,the reference signal comprises one of a STS or a GI. In an aspect, thereference signal comprises a preamble having the non-constant envelope.In an aspect, the means for generating the reference signal having thenon-constant envelope is configured to modulate the reference signal tohave a first dynamic range, the first dynamic range being higher than asecond dynamic range of another signal having a constant envelope. Inone aspect, the apparatus 802/802′ further includes means for receiving,from the receiver, feedback associated with the nonlinearity estimation,and means for performing at least one DPD operation based on thefeedback. In one aspect, the means for performing at least one DPDoperation based on the feedback is configured to adjust one or morecoefficients associated with at least one of a HPA or a DAC.

The aforementioned means may be one or more of the aforementionedcomponents of the apparatus 802 and/or the processing system 914 of theapparatus 802′ configured to perform the functions recited by theaforementioned means. As described supra, the processing system 914 mayinclude the TX Processor 316, the RX Processor 370, and thecontroller/processor 375. As such, in one configuration, theaforementioned means may be the TX Processor 316, the RX Processor 370,and the controller/processor 375 configured to perform the functionsrecited by the aforementioned means.

FIG. 10 is a conceptual data flow diagram 1000 illustrating the dataflow between different means/components in an exemplary apparatus 1002.The apparatus may be a transmitter, such as a UE. The apparatus 1002 mayinclude a reception component 1004, e.g., to receive signals from a basestation 1050. The apparatus 1002 may include a transmission component1010, e.g., to transmit signals to the base station 1050.

The reception component 1004 may receive, from the base station 1050, areference signal having a non-constant envelope. The reception component1004 may provide the reference signal to a signal component 1008. In oneaspect, the reference signal may include a PSS. In one aspect, the PSSmay be based on a Zadoff-Chu sequence. In one aspect, the referencesignal includes at least one of an STS and/or a GI. In one aspect, thereference signal comprises a preamble having the non-constant envelope.

The signal component 1008 may estimate at least one nonlinearitycharacteristic based on the reference signal having the non-constantenvelope. In one aspect, the signal component 1008 may estimate the atleast one nonlinearity characteristic based on a least-squaresalgorithm.

The signal component 1008 may provide the at least one nonlinearitycharacteristic to the feedback component 1006. In one aspect, thefeedback component 1006 may generate feedback based on the at least onenonlinearity characteristic. The feedback component 1006 may provide thefeedback to the transmission component 1010 for transmission to the basestation 1050.

In one aspect, the feedback component 1006 may perform at least one DPoDoperation based on the at least one nonlinearity characteristic. Thefeedback component 1006 may perform at least one DPoD operation byadjusting one or more coefficients associated with at least one of anLNA and/or an ADC. The adjusted coefficients may be used for receivingadditional signals from the base station 1050.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowcharts of FIG. 7. Assuch, each block in the aforementioned flowcharts of FIG. 7 may beperformed by a component and the apparatus may include one or more ofthose components. The components may be one or more hardware componentsspecifically configured to carry out the stated processes/algorithm,implemented by a processor configured to perform the statedprocesses/algorithm, stored within a computer-readable medium forimplementation by a processor, or some combination thereof.

FIG. 11 is a diagram 1100 illustrating an example of a hardwareimplementation for an apparatus 1002′ employing a processing system1114. The processing system 1114 may be implemented with a busarchitecture, represented generally by the bus 1124. The bus 1124 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 1114 and the overalldesign constraints. The bus 1124 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 1104, the components 1004, 1006, 1008, 1010 and thecomputer-readable medium/memory 1106. The bus 1124 may also link variousother circuits such as timing sources, peripherals, voltage regulators,and power management circuits, which are well known in the art, andtherefore, will not be described any further.

The processing system 1114 may be coupled to a transceiver 1110. Thetransceiver 1110 is coupled to one or more antennas 1120. Thetransceiver 1110 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 1110 receives asignal from the one or more antennas 1120, extracts information from thereceived signal, and provides the extracted information to theprocessing system 1114, specifically the reception component 1004. Inaddition, the transceiver 1110 receives information from the processingsystem 1114, specifically the transmission component 1010, and based onthe received information, generates a signal to be applied to the one ormore antennas 1120. The processing system 1114 includes a processor 1104coupled to a computer-readable medium/memory 1106. The processor 1104 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium/memory 1106. The software, whenexecuted by the processor 1104, causes the processing system 1114 toperform the various functions described supra for any particularapparatus. The computer-readable medium/memory 1106 may also be used forstoring data that is manipulated by the processor 1104 when executingsoftware. The processing system 1114 further includes at least one ofthe components 1004, 1006, 1008, 1010. The components may be softwarecomponents running in the processor 1104, resident/stored in thecomputer readable medium/memory 1106, one or more hardware componentscoupled to the processor 1104, or some combination thereof. Theprocessing system 1114 may be a component of the UE 350 and may includethe memory 360 and/or at least one of the TX processor 368, the RXprocessor 356, and the controller/processor 359.

In one configuration, the apparatus 1002/1002′ for wirelesscommunication includes means for receiving, from a receiver, feedbackassociated with the nonlinearity estimation. The apparatus 1002/1002′may include means for receiving a reference signal having a non-constantenvelope. The apparatus 1002/1002′ may include means for estimating atleast one nonlinearity characteristic based on the reference signalhaving the non-constant envelope. The apparatus 1002/1002′ may includeat least one of: means for transmitting feedback based on the at leastone nonlinearity characteristic, or means for performing at least oneDPoD operation based on the at least one nonlinearity characteristic. Inan aspect, the reference signal comprises a primary synchronizationsignal. In an aspect, the primary synchronization signal is based on aZadoff-Chu sequence. In an aspect, the reference signal comprises one ofa STS or a GI. In an aspect, the reference signal comprises a preamblehaving the non-constant envelope. In an aspect, the estimating the atleast one nonlinearity characteristic based on the reference signalhaving the non-constant envelope is based on a least-squares algorithm.In an aspect, means for performing the at least one DPoD operation basedon the at least one nonlinearity characteristic is configured to adjustone or more coefficients associated with at least one of a LNA or anADC.

The aforementioned means may be one or more of the aforementionedcomponents of the apparatus 1002 and/or the processing system 1114 ofthe apparatus 1002′ configured to perform the functions recited by theaforementioned means. As described supra, the processing system 1114 mayinclude the TX Processor 368, the RX Processor 356, and thecontroller/processor 359. As such, in one configuration, theaforementioned means may be the TX Processor 368, the RX Processor 356,and the controller/processor 359 configured to perform the functionsrecited by the aforementioned means.

It is understood that the specific order or hierarchy of blocks in theprocesses/flowcharts disclosed is an illustration of exemplaryapproaches. Based upon design preferences, it is understood that thespecific order or hierarchy of blocks in the processes/flowcharts may berearranged. Further, some blocks may be combined or omitted. Theaccompanying method claims present elements of the various blocks in asample order, and are not meant to be limited to the specific order orhierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” The word “exemplary” is used hereinto mean “serving as an example, instance, or illustration.” Any aspectdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects. Unless specifically statedotherwise, the term “some” refers to one or more. Combinations such as“at least one of A, B, or C,” “one or more of A, B, or C,” “at least oneof A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or anycombination thereof” include any combination of A, B, and/or C, and mayinclude multiples of A, multiples of B, or multiples of C. Specifically,combinations such as “at least one of A, B, or C,” “one or more of A, B,or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and“A, B, C, or any combination thereof” may be A only, B only, C only, Aand B, A and C, B and C, or A and B and C, where any such combinationsmay contain one or more member or members of A, B, or C. All structuraland functional equivalents to the elements of the various aspectsdescribed throughout this disclosure that are known or later come to beknown to those of ordinary skill in the art are expressly incorporatedherein by reference and are intended to be encompassed by the claims.Moreover, nothing disclosed herein is intended to be dedicated to thepublic regardless of whether such disclosure is explicitly recited inthe claims. The words “module,” “mechanism,” “element,” “device,” andthe like may not be a substitute for the word “means.” As such, no claimelement is to be construed as a means plus function unless the elementis expressly recited using the phrase “means for.”

What is claimed is:
 1. A method of wireless communication for a firstwireless communications device, comprising: receiving a signal having anon-constant envelope from a second wireless communications device, thesignal having the non-constant envelope being modulated to have a firstdynamic range that is higher than a second dynamic range of anothersignal having a constant envelope; and determining nonlinearityinformation based on the signal having the non-constant envelope.
 2. Themethod of claim 1, wherein the signal having the non-constant envelopefurther has a non-constant amplitude.
 3. The method of claim 1, furthercomprising: estimating a set of nonlinearity characteristics ornonlinearity constants based on the signal having the non-constantenvelope, wherein the nonlinearity information comprises the set ofnonlinearity characteristics or nonlinearity constants.
 4. The method ofclaim 3, further comprising: adjusting at least one of an amplifier oran analog-to-digital converter (ADC) based on the set of nonlinearitycharacteristics or nonlinearity constants.
 5. The method of claim 1,further comprising: receiving information from the second wirelesscommunications device; and reducing distortion associated with theinformation based on the nonlinearity information.
 6. The method ofclaim 5, further comprising: applying at least one digital postdistortion (DPoD) operation to the information based on the nonlinearityinformation, wherein the distortion is reduced based on the at least oneDPoD operation applied to the information.
 7. The method of claim 5,wherein the signal having the non-constant envelope comprises a preambleassociated with the information.
 8. The method of claim 1, furthercomprising: transmitting the nonlinearity information to the secondwireless communications device; and receiving information from thesecond wireless communications device based on the nonlinearityinformation.
 9. The method of claim 1, wherein the signal comprises atleast one of a reference signal, a synchronization signal, a pilotsignal, or a training sequence.
 10. The method of claim 1, wherein thesignal having the non-constant envelope is modulated using phase-keyshifting.
 11. An apparatus for wireless communications, comprising: amemory; and at least one processor coupled to the memory and configuredto: receive a signal having a non-constant envelope from a secondwireless communications device, the signal having the non-constantenvelope being modulated to have a first dynamic range that is higherthan a second dynamic range of another signal having a constantenvelope; and determine nonlinearity information based on the signalhaving the non-constant envelope.
 12. The apparatus of claim 11, whereinthe signal having the non-constant envelope further has a non-constantamplitude.
 13. The apparatus of claim 11, wherein the at least oneprocessor is further configured to: estimate a set of nonlinearitycharacteristics or nonlinearity constants based on the signal having thenon-constant envelope, wherein the nonlinearity information comprisesthe set of nonlinearity characteristics or nonlinearity constants. 14.The apparatus of claim 13, wherein the at least one processor is furtherconfigured to: adjust at least one of an amplifier or ananalog-to-digital converter (ADC) based on the set of nonlinearitycharacteristics or nonlinearity constants.
 15. The apparatus of claim11, wherein the at least one processor is further configured to: receiveinformation from the second wireless communications device; and reducedistortion associated with the information based on the nonlinearityinformation.
 16. The apparatus of claim 15, wherein the at least oneprocessor is further configured to: apply at least one digital postdistortion (DPoD) operation to the information based on the nonlinearityinformation, wherein the distortion is reduced based on the at least oneDPoD operation applied to the information.
 17. The apparatus of claim15, wherein the signal having the non-constant envelope comprises apreamble associated with the information.
 18. The apparatus of claim 11,wherein the at least one processor is further configured to: transmitthe nonlinearity information to the second wireless communicationsdevice; and receive information from the second wireless communicationsdevice based on the nonlinearity information.
 19. The apparatus of claim11, wherein the signal comprises at least one of a reference signal, asynchronization signal, a pilot signal, or a training sequence.
 20. Anon-transitory, computer-readable medium storing computer-executablecode for wireless communications, the code when executed by a processorcause the processor to: receive a signal having a non-constant envelopefrom a second wireless communications device, the signal having thenon-constant envelope being modulated to have a first dynamic range thatis higher than a second dynamic range of another signal having aconstant envelope; and determine nonlinearity information based on thesignal having the non-constant envelope.